(a) Wastewater is passed through bar screens. Large objects like rags, sticks, cans, plastic packets, napkins are removed.
(b) Water then goes to a grit and sand removal tank. The speed of the incoming wastewater is decreased to allow sand, grit and pebbles to settle down.
(c)The water is then allow to settle in a large tank which is sloped towards the middle. Solids like faeces settle at the bottom and are removed with a scraper. This is the sludge. A skimmer removes the floatable solids like oil and grease. Water so cleared is called clarified water. The sludge is transferred to a separate tank where it is decomposed by the anaerobic bacteria. The biogas produced in the process can be used as fuel or can be used to produce electricity.
(d) Airis pumped into the clarified water to help aerobic bacteria to grow. Bacteria consume human waste, food waste, soaps and other unwanted matter still remaining in clarified water.
(e) After several hours, the suspended microbes settle at the bottom of the tank as activated sludge. The water is then removed from the top.

Organic impurities: Human faeces, Animal wastes, oil, urea (urine), pesticides, herbicides.
Inorganic impurities: Nitrates, phosphates, metals.
Disease causing microbes: Microbes which cause typhoid, cholera, polio, dysentery.

(i) Left overfood contains lot of oil and fat, it should not be thrown down the drain. They choke the pipe when they become harden. These waste when thrown in open drains block the oil pores thereby decreasing its effectiveness to filter water. Such wastes should be thrown in dustbin only.
(ii) Solid wastes such as used tea leaves, plastic bags, soft toys, cotton and sanitary towels should not be thrown in drains. Such wastes block the drain. They reduce free flow of oxygen and thus slow down the process of degradation.
(iii) Chemical products like medicines, motor oil, paint, machine oil and insecticide should also be not thrown down the drain. These substances kill water purifying organisms and hamper degradation.

Treatment of waste water involves physical, chemical and biological processes which remove physical, chemical and biological matter that contaminate waste water.
These steps are as follows :
(i)Waste water is passed through bar screens. Large objects like rages, sticks, cans, plastic packets, napkins get removed.
(ii) Waste water then goes to a grit and sand removal tank. In this the speed of the waste water is reduced to allow, sand grit and pebbles to settle down.
(iii) The water is then allowed to settle in a large tank which is sloped towards the middle solids like faeces settle down at the bottom and are removed by a scrapper. A skimmer removes the floatable solids like oil and grease. The sludge is then transferred to another tank where it is decomposed by anaerobic bacteria.
(iv) Then air is passed through clarified water to allow aerobic bacteria to grow, which consume the remaining organic waste. This water is then released into the water bodies.

We can minimise waste and pollutants entering the water and create less wastewater by taking following few steps at home:
(i) By not throwing used tea leaves, solid food remains, etc., in the drain. We should throw it in the dustbin.
(ii) By not throwing chemicals like medicines, paints, insecticides, etc., in the drain as they increase the pollution load of the sewage

(a) Typhoid and cholera.
(b) In vermi-composting toilets, human excreta is treated by earthworms in a pit.
(c) He is intelligent and concious about health

In the vermi-processing toilet, the human excreta is treated by earthworms in a pit. The earthworms gradually eat up all the organic matter present in human excreta, decompose it and pass out from their body in the form of warm casting (also called vermi cakes).
The useful product obtained from a vermi-processing toilet is vermi cakes which is kind of high quality manure.

(i) Inorganic impurities - nitrates, phosphates and metals.
(ii) Organic impurities - fruit and vegetable wastes, oil, urea, human faeces, animal waste, pesticides and herbicides